Final Flashcards
How does a transporter reduce the activation energy in simple diffusion?
by forming non-covalent interactions with the dehydrated solute to replace the hydrogen bonding with water and by providing a hydrophilic transmembrane pathway.
What is the differences between channels and Active transporters?
Channels rate of flux is very fast and you cant saturate them. Once they open, anything can flow in/out. They are closed either by having a ligand bind or make it voltage-gated.
Transporters respond to the solutes they’re transporting by changing shape, whereas channels do not.
What are the conformations of the GLUT transporter?
T1, with the glucose-binding site exposed on the outer surface of the plasma membrane, and T2, with the binding site exposed on the inner surface.
What is the mechanism of glucose transport?
- Glucose in blood plasma binds to a stereospecific site on T1; this lowers the activation energy for
- a conformational change from glucoseout • T1 to glucosein • T2, affecting the transmembrane passage of the glucose.
- Glucose is released from T2 into the cytoplasm, and
- the transporter returns to the T1 conformation, ready to transport another glucose molecule.
Why do we not want glucose transport to max out in the liver?
We don’t want the glucose transporter to be maxed out in the liver b/c you want to be able to transport a large sum of glucose out of the cell into the muscles that need it
How is CO2 transported in Erythrocytes and lungs?
CO2 diffuses in and is converted to bicarbonate by carbonic anhydrase. We transport bicarb out and chloride in.
In the lungs, this process is reversed. The bicarb comes in from blood plasma and chloride is taken out.
What is the goal of the bicarb antiporter?
This cotransport system allows the entry and exit of HCO3- without changing the membrane potential. Its role is to increase the CO2-carrying capacity of the blood.
Why is energy needed in active transport?
Accumulation of solutes above an equilibrium point.
Endergonic deltaG is positive, thus it Requires energy to move solutes up a concentration gradient
what is the problem with vanadate?
Vanadate can bind, and block the P-Type ATPase, thus there will be no phosphorylation b/c the enzyme can only cleave a phosphate bond
What is the SERCA Pump?
an integral membrane protein that moves Ca2+ out of the cell membrane and into the ER lumen
What is the mechechanisum of the SERCA Pump?
Primary active transporter: ATP binds to its nucleotide domain, and then calcium comes in, but it gets stuck in the middle of the protein because it’s too big.
We hydrolyze ATP to ADP and phosphorylate the transporter and this changes its conformation, and the calcium is released into the lumen.
ADP falls off and becomes de-phosphorylated, and we change back into the original confirmation and do it the process again
What is the purpose of the Na/K+ ATPase?
Primary active antiporter that Maintains ECG in all our neurons by Pumping K against its concentration from inside the cell to out of the cell and sodium comes in.
What is the mechanism of Na/K+ ATPase?
In the absence of ATP, protein is facing inside the cell, and it likes sodium and it will pick up any sodium.
We phosphorylates and ATP binds and we change our confirmation and face outside, and now the protein hates sodium and it releases sodium.
so potassium will bind and then we will de-phosphorylate and change our confirmation, and we will do this back and forth creating an ECG
What is the role of ouabain?
With 2 sodium bound on the extracellular side, there is no way K+ can come in, de-establishing the electrical potential
What is the role of Palytoxin?
Locks protein so that ion-binding sites open on both sides, and K+ can exit, thus, it deflates the ion gradient
How does Digitalis work?
Digitalis is used to treat congestive heart failure (their heart isn’t pumping well enough so blood doesn’t flow well) by inhibiting sodium influx and raising sodium intracellular enough that the sodium-calcium pump when it transports it creates a much harder contraction
What are the parts of the F-type ATPase?
Fo = integral membrane protein complex F1 = peripheral protein that uses the energy of ATP to drive protons uphill.
How is ATP generated generally in transport?
If you pumped proton to the mitochondrial matrix your hydrolyzing ATP and If you are pumping it out of the mitochondria, you are making ATP
What are ABC Transporters?
ATP-dependent transporters - Pump amino acids, peptides, proteins, metal ions, some lipids, bile salts out of cell against a concentration gradient.
2 nucleotide binding domains (NBD) and transmembrane
Most act as pumps, some act as ion channels that open and close with ATP hydrolysis.
What is the mechanism of ABC Transporter?
Substrate binds to the transporter on the cytoplasmic side, with ATP bound to the NBD sites.
On substrate binding and ATP hydrolysis to ADP, a conformational change exposes the substrate to the outside surface and lowers the affinity of the transporter for its substrate diffuses away from the transporter and into the extracellular space.
What is lactose permease?
a monomer secondary active transporter. Lactose permease is the transporter for lactose and is a transmembrane protein.
It transports one proton and one lactose into the cell. It is a symporter. The protons were established through the oxidative phosphorylation pathway
How does CN inhibit lactose permease?
CN binds to the last transporter of the ETC and inhibits the lactose permease
Lactose can still be transporter on the permease but it is a facilitated diffusion, and it will saturate easily b/c you cant get it across the membrane with CN inhibiting the establishment of the proton gradient
How else can lactose permease be inhibited?
We can also inhibit it by Arg and Glu which has a carboxylic acid and amino groups that can be protonated. Protons are transported by hoping across membrane by interacting with a proton. As the proton is coming through, it is binding to glut and arg changing the conformation, so lactose can come in really easily
Describe Glucose transporter in the intestinal cells?
Glucose is cotransported with Na+ across the apical plasma membrane into the epithelial cell. It moves through the cell to the basal surface, where it passes into the blood via GLUT2, a passive glucose uniporter. The Na+K+ ATPase continues to pump Na+ outward to maintain the Na+ gradient that drives glucose uptake.
sodium doesn’t affect the transporter b/c it’s not secondary active
How is water transported?
through Aquaporins; an Integral membrane protein with 4 monomers associated in a tetramer to form a pore
What is the purpose of NPA in the aquaporin ?
NPA = asparagine, proline, and alanine. Hydroxonium ion wouldn’t get close to this sequence. It helps the structure to filter out, so that only water come in and not any hydronium ions
What are the types of ion-selective channels?
Ligand-gated and Voltage-gated channels
How is K+ channel selective for only potassium?
Carbonyl groups line the walls of the pore of the selectivity filter to balance out the charge. 4 rigid protein groups form a selectivity filter, which makes the filtered highly selective for potassium over sodium ions
How does voltage-gated channel filter solutes?
When positively charged, the gate is open and sodium can come through. The channel will depolarize and the gates will close, and sodium cant go out
Why do we need ammonia channels?
We need ammonium channels b/c ammonia in water is usually charged and its NH4
How do toxins work?
they bind to voltage-gated sodium-potassium channels, disrupting the gradient
How does cystic fibrosis occur?
70% of patients have a deletion of a phenylamine (just 1) causing the protein to misfolded so it can’t insert into the membrane. The outer membrane becomes sticky because you don’t have water
What is oxidative phosphorylation?
Reduction of O2 to H2O in the mitochondria from Electrons donated by NADH or FADH2
What are the 3 stages of cellular respiration?
Stage 1: oxidation of fatty acids, glucose, and some amino acids yields acetyl-CoA.
Stage 2: oxidation of acetyl groups in the citric acid cycle includes four steps in which electrons are abstracted.
Stage 3: electrons carried by NADH and FADH2 are funneled into a chain of mitochondrial (or, in bacteria, plasma membrane-bound) electron carriers—the respiratory chain—ultimately reducing O2 to H2O. This electron flow drives the production of ATP.
How is ADP converted to ATP?
Electrons flow through a chain of membrane bound carriers
Free energy from the electron flow is coupled to the transport of protons across membrane.
Transmembrane flow of protons down their concentration gradient leads to synthesis of ATP.
What is needed of the membrane for ATP synthesis?
The membrane must contain proteins that couple the “downhill” flow of electrons in the electron-transfer chain with the “uphill” flow of protons across the membrane.
The membrane must contain a protein that couples the “downhill” flow of protons to the phosphorylation of ADP.
What is Ubiquinone?
Ubiquinone is a lipid-soluble conjugated dicarbonyl compound that readily accepts electrons
Upon accepting two electrons, it picks up two protons to give an alcohol –> ubiquinol
What is the sequence of electron carriers?
NADH/C1 to Q, Q to C3, C3 to Ctyo C, Cyto C to C4, C4 to O2
FADH2/C2 to Q, Q to C3, C3 to Cyto C, Cyto C to C4, C4 to O2
What happens in NADH/ubiquinone oxidoreductase/Complex I?
NADH becomes oxidized to NAD and its 2e’ gets transferred to Q and Q becomes QH2. complex 1 pumps 4 protons for every NADH that is oxidized
What is the difference between FADH2 and NADH
WHEN FADH2 GETS OXIDIED, YOU DON’T GET ANY PROTONS PUMPED CROSS, AND THUS IT DOESN’T allow you to make more ATP which is why NADH is a better
Ubiquinone is the branch point . If you start with FADH2 you don’t use complex 1, but if you’re using NADH you start at complex 1 and you will transfer the electrons to Q which becomes QH2 (ubiquinol)
What is Succinate Dehydrogenase/Complex II?
Q GOES TO QH2 TO REGENERATE FUMARATE BACK TO SUCCINATE TO CONTINUE THE CIRTIC ACID CYCLE
SUCCINATE DOES NOT PUMP PROTONS, ITS JUST TRYING TO regenerate FAD TO FADH2.
What is the role of heme in complex II?
The hemebis not on the main path of electron transfer but protects against the formation of reactive oxygen species (ROS) by electrons that go astray.
